In the fabrication of integrated circuit devices, often there is a need to form conductive metal structures by filling trenches, holes or other openings in a substrate (or in layers of the substrate). In addition to traditional filled structures such as vias and contact holes, the filling processes are becoming more widely used with the wider use of damascene techniques for forming conductive structures such as metal wiring lines and dual damascene techniques which can be used to form compound conductive structures.
Most techniques for filling openings in substrates involve the use of chemical vapor deposition (CVD) and/or physical vapor deposition (PVD) of the desired metals in an opening which has been lined with a conductive barrier layer such as TiN. In many instances, these metal deposition techniques are supplemented with reflow techniques whereby deposited metal is heated to cause flow of the metal into voids remaining in the structure and/or to give the deposited metal a more planar profile. In some instances, additional steps such as etching may be used between deposition steps to access voids which are otherwise sealed off. In general, it is desired to reduce or eliminate the occurrence of voids in the filled structure, to minimize the number of steps needed to obtain the desired filled structure, to minimize the process temperature needed to achieve the filled structure, etc.
With the continued shrinking of integrated circuit device dimensions, the challenge of adequately filling the openings to form the desired conductive structures becomes greater. The challenge is typically greatest where the structure to be filled has a narrow opening and a high aspect ratio (ratio of depth to opening width). One approach to improved structure filling has been a two step process involving the formation of a continuous conformal CVD metal layer in the opening to be filled followed by deposition and reflow of a PVD metal layer. This technique is generally described in published European Patent Application No. 0 776 037, the disclosure of which is incorporated herein by reference.
While the above CVD/PVD technique provides good filling for many structures, there remains a concern regarding structures having less than 250 nm opening width since CVD processes tend to cause a closing off at the top of the opening. In addition to this concern, there is a continuing desire for further improved techniques which provide the ability to fill structures having high aspect ratios in an economical and reliable manner.